Typically wet (or "flooded electrolyte") lead-acid batteries have a rectangular shaped container onto which a cover assembly is sealed. Both parts usually are made of an injected molded thermoplastic polymer, such as polypropylene. The interior of the battery generally is divided by partition walls into cells, each of which contains an electrode stack. Once the cover assembly is sealed to the container, the cells are filled with electrolyte, typically through process holes in the cover assembly which are associated with each cell. The electrode stacks are electrically connected in series by intercell connections usually extending through the partition walls.
It is important to form the partition walls and intercell connectors so that the cells provide a leak-proof receptacle for electrolyte. That is, if electrolyte seepage occurs between the cells, by whatever route, an electrical circuit might be completed --the cells "self-discharge" or "short circuit". This phenomenon can lead to loss of charge and premature failure of the battery. Despite the general efficacy of modern manufacturing techniques, leak-proof cells are not always formed. Accordingly, it is important to test the battery once the intercell connectors have been formed and the cover sealed to ensure that leaks do not exist between the cells.
A common technique is to "pressure check" each individual cell. In essence, it is a simple procedure. The test equipment commonly employed comprises a cup-like pressure head tip which may be placed over the uncapped process holes in an airtight fashion. Air is pumped into the cell through the cup, and the air pressure is monitored for a period of time.
Wet batteries also must comprise some means by which gas generated during charging, predominately hydrogen and oxygen, are vented to the ambient. Hydrogen and oxygen gas create an obvious potential for explosion; and, thus, the battery's venting system should permit substantially complete evacuation of generated gases.
In wet batteries, there are large quantities of free electrolyte in the cell, which can slosh and splash about the interior of the battery during shipment, installation, and use of the battery. The venting system, therefore, not only must allow gases to vent, but it also must prevent electrolyte from escaping from the battery.
One popular type of venting system generally comprises internal apertures, trapping chambers, and external exhaust ports associated with each cell. Gases generated within the battery vent through one or more internal apertures into the trapping chamber. The trapping chamber is provided with a variety of baffles and internal restrictions designed to prevent electrolyte from escaping through the trapping chamber and to condense and collect electrolyte mist and vapor. Trapping chambers also typically include sloping floors and sumps designed to reflux trapped electrolyte back through the internal apertures to the cells. The internally generated gases, stripped of entrained electrolyte, eventually pass to the ambient through the exhaust port.
The trapping chambers associated with each cell often are manifolded, most frequently in sets of three or six, so as to share common exhaust ports. This not only provides a simpler design and reduces the number of flame arrestors needed, a common element associated with each exhaust port, but provides for more efficient electrolyte collection. Thus, especially for the remote cells in the manifolded system, entrained or flowing electrolyte simply has much farther to go before it can "escape" the system.
Such venting systems, however, necessitate the use of a multiple component cover assembly, i.e., a primary cover which is sealed to the battery container and one or more additional cover pieces which are sealed to the primary cover to complete the formation of the venting system. Preferably, the cover pieces are sealed to the primary cover before the primary cover is sealed to the container. That preference becomes clear in light of conditions existing in the modern battery industry.
Because lead is both very heavy and a major component of lead-acid batteries, it is necessary to maintain a large number of battery assembly facilities each supplying a relatively limited distribution/consumer area in order to keep shipping expenses within reason. A single plastics molding plant, however, can efficiently and economically provide many battery assembly plants with containers, covers, and other thermoplastic battery components. Indeed, it is more efficient to complete the cover assembly in the plastics molding plant because this avoids the need to install specialized machinery for completing the cover assembly in each battery assembly plant. It also is preferable to minimize the amount of sealing done in the battery assembly plants because sulfuric acid electrolyte permeates those facilities and everything in them and can interfere with the sealing process, making such processes less efficient.
In summary, therefore, there are a number of needs which preferably are satisfied by wet, lead-acid storage batteries and/or their venting systems: (1) capacity for pressure checking individual cells; (2) manifolding of trapping chambers so as to improve the efficiency of the venting system; and (3) completion of the cover assembly before it is sealed to the container. Unfortunately, prior art designs have not succeeded in satisfying all of those needs by a single design.
So-called "gang vent plugs" sometimes are used to vent gases, and it may be possible to pressure check individual cells in a battery which utilizes gang vent plugs. If properly designed, gang vent plugs also may provide acceptable venting and electrolyte separation efficiency. Such gang vent plugs also can be completely assembled before the primary cover is sealed to the battery container. Electrolyte leakage, however, can be a problem.
Gang vent plugs "plug" into the process holes through which the battery is filled with electrolyte. That is, they are adapted to cap several, usually three or six, of the process holes. Unfortunately, the tolerances required in manufacturing gang vent plugs are close and can be difficult to coordinate.
Such tolerances must be built into the mold to allow for shrinking of the plastic during the molding process. In gang vent plugs, the manufacturer must provide tolerances not only between the diameters of the plugs and the process holes, but also in the alignment of the centers of the plugs and process holes --both in the context of a relatively long piece of plastic. Building such tolerances into a gang vent plug is difficult, and can result in the formation of a less than effective seal in one or more of the process holes. For that reason, gang vent plugs provide an incomplete solution to these problems facing the industry.
On the other hand, batteries such as those disclosed in U.S. Pat. No. 4,486,516 to D. Poe and U.S. Pat. No. 4,278,742 to T. Oxenreider et al. have individual process hole caps, which can be more reliably molded, and those batteries also have manifolded trapping chambers. Pressure checking individual cells in such batteries by conventional equipment, however, is not possible regardless of whether the cover assembly, or only the primary cover, is sealed to the container prior to testing.
It is an object of the present invention, therefore, to provide a cover assembly for a wet battery which comprises a manifolded venting system, wherein the components of the cover assembly can be sealed together before the assembled cover is sealed to the battery, and wherein the cells of the battery can be individually pressure checked as well.
It is also an object of this invention to provide a battery, and a cover assembly for such a battery, that includes a venting system which efficiently vents gases and separates electrolyte, but which is more easily manufactured and does not interfere with pressure checking of individual cells of the battery.
Another object is to provide a battery wherein the process holes are more efficiently capped.
Finally, it is another object of the subject invention to provide a battery wherein all of the above advantages are realized.
Those and other objects will become apparent to those of ordinary skill in the art upon inspection of the drawings and reading of the description which follows.